Whey proteins are a kind of milk protein and composed of lactalbumin, lactoglobulin, etc., and they are denatured by heating at 72 to 75.degree. C. Utilization of whey proteins for foods has been studied in view of their properties, such as solubility, emulsifiability, gelling ability, etc. Recently, it has been proposed to use whey proteins particularly for textured substances as fat substitutes.
Fat substitutes using proteins are roughly divided into gel compositions and emulsion-like compositions. Most of the emulsion-like compositions using whey proteins known so far are in the form of microparticles produced by heating for denaturation or using high shearing force. Singer et al. disclose denatured protein microparticles for fat substitutes prepared from whey proteins (JP-A 63-24857, U.S. Pat. No. 4,734,287). These microparticles are giant colloids of spherical particles formed by heating a whey protein aqueous solution under high shearing conditions. U.S. Pat. No. 4,143,174 discloses use of colloidal precipitates obtained from a whey solution for foods. These are non-proteinaceous colloidal insoluble precipitates formed by heating and raising pH of a concentrated permeate fraction of ultra-filtration of whey. For producing proteinaceous microparticles without heating for denaturation, there is a method wherein hydrophobic proteins dissolved in an organic solvent are dispersed in an aqueous solution (JP-A 4-502102, U.S. Pat. No. 246,435). However, because whey proteins are soluble in water, whey proteins cannot be used for this method. Examples of emulsion-like fat substitutes using insoluble salts are microparticles of titanium oxide, microparticles of calcium citrate (JP-A 5-260906, U.S. Pat. No. 5,219,602), etc. However, these salts cannot be completely substituted for fat nor used in foods in a large amount because they provide a rough feel and an astringent taste.
As described above, to form fat substitutes providing an emulsion-like texture by using a whey protein solution, methods wherein proteinaceous microparticles are formed by denaturation by heating under high shearing conditions have often been used. However, most of the proteinaceous microparticles obtained by these methods have rather cream-like properties, and few of them have solid oil and fat-like properties.
Techniques to produce foods by denaturing proteins are well known. In general, denaturing proteins means partially changing the structure of protein molecules so as to change their shapes. During the denaturation of proteins, the deformation, association and aggregation of the protein molecules occur and result in the formation of aggregates. Such association and aggregation are caused by intermolecular bonds of hydrophobic bonds, hydrogen bonds, ionic bonds, etc. It is difficult to understand the relationships among them to expect specific properties of the proteins.